An aerogel, as a high specific area (≧500 m2/g), ultra-porous material having a porosity of about 90% to 99.9% and pores with a diameter of about 1 nm to about 100 nm, has characteristics such as ultra lightweightness, ultra-insulation, and ultra-low dielectric constant. Due to the excellent physical properties, research into the applications of the aerogel as a transparent insulator and an environmentally-friendly high-temperature insulator, an ultra-low dielectric thin film for a highly integrated device, a catalyst and a catalyst support, an electrode for a super capacitor, and an electrode material for desalination as well as the development of an aerogel material has been actively conducted.
The biggest advantage of the aerogel is super-insulation having a thermal conductivity of 0.300 W/m·K or less which is lower than that of an organic insulation material such as a typical Styrofoam. Also, with respect to the aerogel, there is no fire vulnerability and generation of toxic gas in case of fire, i.e., fatal weaknesses of a typical organic insulation material.
The silica aerogel may be broadly categorized into three forms, powder, granules, and monolith, and among them, the powder form is most common.
Silica aerogel powder may be commercialized in a form, such as an aerogel blanket or aerogel sheet, by compositing with fibers. Also, since the blanket or sheet, which is prepared by using a silica aerogel, has flexibility, it may be bent, folded, or cut to a predetermined size or shape. Thus, the silica aerogel may be used in household goods, such as jackets or shoes, as well as industrial applications such as an insulation panel of a liquefied natural gas (LNG) line, an industrial insulation material and a space suit, transportation and vehicles, and an insulation material for power generation. Furthermore, the silica aerogel may be used in a fire door as well as a roof or floor in a home for fire prevention.
In general, a wet gel is prepared from a silica precursor such as water glass or tetraethoxysilane (TEOS), and an aerogel is then prepared by removing a liquid component in the wet gel without destroying its microstructure. In this case, a hollow of the wet gel is filled with water or alcohol. Accordingly, when the solvent is removed by a subsequent drying process, shrinkage and cracking of a pore structure occur due to high surface tension of water at a gas/liquid interface while the liquid phase solvent is evaporated into a gas phase. As a result, a decrease in specific surface area and changes in pore structure may occur in the finally prepared silica aerogel. Thus, in order to maintain the pore structure of the wet gel, there is a need to substitute water or alcohol having high surface tension with an organic solvent having relatively low surface tension. Also, the dried silica aerogel maintains low thermal conductivity immediately after the drying, but the thermal conductivity may gradually increase because a hydrophilic silanol group (Si—OH) present on the surface of silica absorbs water in the air. Therefore, there is a need to modify the surface of the silica aerogel into hydrophobic in order to maintain low thermal conductivity.